The present invention relates to a process for producing a display means by cathodoluminescence excited by field emission or cold emission. It particularly applies to the production of simple matrix displays making it possible to display fixed images or pictures and the production of multiplexed complex screens making it possible to display animated pictures, such as television pictures.
A display means by cathodoluminescence excited by field emission is described in French patent application 84 11986 of July 27 1984 filed in the name of the Applicant. In FIG. 1 is shown an exploded perspective view of the display means described in this document.
The display means comprises a display cell 2, which is tight and placed under vacuum, having two facing glass walls 4, 6. The lower wall 6 of cell 2 is equipped with a first series of parallel conductive strips 8 serving as cathodes and a second series of parallel conductive strips 10 serving as grids. The conductive strips 10 are oriented perpendicular to conductive strips 8 and are insulated from the latter by a continuous insulating coating 12, more particularly of silica.
The end regions 9 of the cathodes 8 not covered by an insulant and not intercepting the grids 10 permit electric contacting on the cathodes.
Conductive strips 8, 10 respectively represent the columns and rows. An elementary display point 14 corresponds to each intersection of a row and column.
The conductive strips or grids 10 and the insulating layer 12 are perforated by a large number of holes 16, which house the electron microguns or microemitters. A plurality of microemitters corresponds to each elementary display point 14.
As shown in FIG. 2, these microemitters are in each case constituted by a metal cone 18 emitting electrons, when an appropriate electric field is applied thereto. These metal cones 18 rest by their base directly on cathodes 8 and the apex of the cones is substantially level with the conductive strips 10. The base diameter of the cones and the height thereof are e.g. approximately 1 .mu.m.
The upper wall 4 of cell 2, as shown in FIG. 1, is provided with a continuous conductive coating 20 serving as the anode. Anode 20 is covered by a coating 22 made from a light emitting material when subject to electrode bombardment from microemitters 18.
The emission of electrons by a microemitter 18 can be brought about by simultaneously polarizing cathode 8 and grids 10, which face one another, as well as anode 20. Anode 20 can in particular be grounded, the grids 10 being raised to the potential of the anode or negatively polarized with respect thereto by means of a voltage source 24. Cathodes 8 are negatively polarized or biased with respect to the grid using a voltage source 26. Cathodes 8 and grids 10 can be sequentially polarized in order to bring about a point-by-point image on the display cell 2. The image is observed from the side of the upper wall 4 of the cell.
The number of microemitters 18 per display point 14, i.e. per intersection of a cathode and a grid is generally high, which makes it possible to have a more uniform emission characteristic between display points (mean value effect). This leads to a certain redundancy of the microemitters, so that it is possible to accept a certain proportion of non-functioning microemitters.
In practice, the number of microemitters is between 10.sup.4 and 10.sup.5 emitters per mm.sup.2. Therefore conventional production requiring a precise positioning of the emitters placing the cathodes and grids would be complex and would increase the cost of the display means.